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<title>表单与v-model</title>
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<h1 id="-v-model">表单与v-model</h1>
<p>Vue.js提供了<code>v-model</code>指令，用于在表单类元素上双向绑定数据。</p>
<p>使用<code>v-model</code>后，表单控件显示的值只依赖所绑定的数据，不再关心初始化时的<code>value</code>属性，对于在<code>&lt;textarea&gt;&lt;/textarea&gt;</code>之间插入的值，也不会生效。</p>
<p>使用<code>v-model</code>时，如果是用中文输入法输入中文，一般在没有选定词组前，也就是在拼音阶段，Vue时不会更新数据的，当敲下汉字时才会触发更新。</p>
<p>如果希望总是实时更新，可以用<code>@input</code>替代<code>v-model</code>。事实上，<code>v-model</code>也是一个特殊的语法糖，只不过它会在不同的表单上智能处理。</p>
<h2 id="-">单选按钮</h2>
<p>单选按钮在单独使用时，不需要<code>v-model</code>，直接使用<code>v-bind</code>把你当一个布尔类型的值，为真时选中，为否时不选。</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;input type=&quot;radio&quot; :checked=&quot;picked&quot; id=&quot;radio&quot;&gt;
    &lt;label for=&quot;radio&quot;&gt;单选按钮&lt;/label&gt;
&lt;/div&gt;
</code></pre><p>如果是组合使用来实现互斥选择的效果，就需要<code>v-model</code>配合<code>value</code>来使用。</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;p&gt;
        &lt;input type=&quot;radio&quot; v-model=&quot;picked&quot; value=&quot;html&quot; id=&quot;html&quot;&gt;
        &lt;label for=&quot;html&quot;&gt;HTML&lt;/label&gt;
    &lt;/p&gt;
    &lt;p&gt;
        &lt;input type=&quot;radio&quot; v-model=&quot;picked&quot; value=&quot;js&quot; id=&quot;js&quot;&gt;
        &lt;label for=&quot;js&quot;&gt;JavaScript&lt;/label&gt;
    &lt;/p&gt;
    &lt;p&gt;
        &lt;input type=&quot;radio&quot; v-model=&quot;picked&quot; value=&quot;css&quot; id=&quot;css&quot;&gt;
        &lt;label for=&quot;css&quot;&gt;CSS&lt;/label&gt;
    &lt;/p&gt;
    &lt;p&gt;选择的项：{{picked}}&lt;/p&gt;
&lt;/div&gt;
</code></pre><h2 id="-">复选框</h2>
<p>复选框单独使用时，也是用<code>v-model</code>绑定一个布尔值。</p>
<p>组合使用时，也是<code>v-model</code>与<code>value</code>一起，多个勾选框都绑定到同一个数组类型的数据，<code>value</code>的值在数组中，就会选中这一项。这一过程也是双向的，在勾选时<code>value</code>得知也会自动<code>push</code>到这个数组中。</p>
<h2 id="-">选择列表</h2>
<p>选择列表就是下来选择器，分为单选和多选两种方式。</p>
<p><option>是备选项，如果含有<code>value</code>属性，<code>v-model</code>就会优先匹配<code>value</code>值；如果没有，就会直接匹配<code>&lt;option&gt;</code>的<code>text</code>。</p>
<p>在业务中，<code>&lt;option&gt;</code>经常用<code>v-for</code>动态输出，<code>value</code>和<code>text</code>也是用<code>v-bind</code>动态输出。</p>
<h1 id="-">绑定值</h1>
<p>在业务中，有时需要绑定一个动态的数据，这时可以使用<code>v-bind</code>实现。</p>
<h2 id="-">单选按钮</h2>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;input type=&quot;radio&quot; v-model=&quot;picked&quot; :value=&quot;value&quot;&gt;
    &lt;p&gt;{{picked}}&lt;/p&gt;
    &lt;p&gt;{{value}}&lt;/p&gt;
&lt;/div&gt;

data: {
    picked: false,
    value: 123
},
</code></pre><p>在选中时，<code>app.picked===app.value</code>，值都是<code>123</code>。</p>
<h2 id="-">复选框</h2>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;input type=&quot;checkbox&quot; v-model=&quot;toggle&quot; :true-value=&quot;value1&quot; :false-value=&quot;value2&quot;&gt;
    &lt;p&gt;{{toggle}}&lt;/p&gt;
    &lt;p&gt;{{value1}}&lt;/p&gt;
    &lt;p&gt;{{value2}}&lt;/p&gt;
&lt;/div&gt;
</code></pre><h2 id="-">选择列表</h2>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;select v-model=&quot;selected&quot;&gt;
        &lt;option :value=&quot;{number:123}&quot;&gt;123&lt;/option&gt;
    &lt;/select&gt;
    {{selected.number}}
&lt;/div&gt;
</code></pre><p>当选中时，<code>app.selected</code>是一个Object，所以<code>app.selected.number===123</code>。</p>
<h1 id="-">修饰符</h1>
<p>与事件的修饰符类似，<code>v-model</code>也有修饰符，用于控制数据同步的时机。</p>
<h2 id="-lazy-"><code>.lazy</code></h2>
<p>在输入框中，<code>v-model</code>默认是在<code>input</code>事件中同步输入框的数据，使用修饰符<code>.lazy</code>会转变为在<code>change</code>事件中同步。</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;input type=&quot;text&quot; v-model.lazy=&quot;message&quot;&gt;
    &lt;p&gt;{{message}}&lt;/p&gt;
&lt;/div&gt;
</code></pre><p>这时，<code>message</code>并不是实时变化，而是在失焦或按回车键时才更新。</p>
<h2 id="-number-"><code>.number</code></h2>
<p>使用修饰符<code>.number</code>可以将输入转换成Number类型，否则输入的数字，但它的类型其实是String，在数字输入框时比较有用。</p>
<pre><code>&lt;div id=&quot;app&quot;&gt;
    &lt;input type=&quot;number&quot; v-model.number=&quot;message&quot;&gt;
    &lt;p&gt;{{typeof message}}&lt;/p&gt;
&lt;/div&gt;
</code></pre><h2 id="-trim-"><code>.trim</code></h2>
<p>修饰符<code>.trim</code>可以自动过滤输入的首尾空格。</p>
<pre><code>&lt;input type=&quot;text&quot; v-model.trim=&quot;message&quot;&gt;
</code></pre>
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